Generically calling a method on an object

Question

Hello,
I am trying to write a small utility method to generically call a method on an object.
This is what I have.
    public static void doCall(Object o, String methodName, Object ... args){
        Class[] types = new Class[args.length];
        int i = 0;
        for(Object arg : args){
            types[i] = arg.getClass();
        try {
            Method m = o.getClass().getMethod(methodName, types);
            m.invoke(o, args);
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException("Error dynamically calling method " + methodName + " on " + o.toString());
    }It doesn't work because it can't find the method. If I hard code the parameter types as "new Object[] {Double.TYPE}" it works fine (on methods that take a double).
So, my question is, how can I generically set up the parameter types based on the types of the arguments?
Thanks,
~Eric

Answer 1

The problem is not on calling agr.getClass(), your primitive double is already autoboxed to a Double object. It is the doCall(...) method who expects an object, not a primitive. So when giving it a primitive value, java autoboxes it to the corresponding object type.
This means your attempt will only work if the methods to call do not have any primitives as parameters.
Test this code:
public class GenericMethodCaller {
     public static void doCall(Object o, String methodName, Object ... args){
        Class[] types = new Class[args.length];
        int i = 0;
        for(Object arg : args){
            types[i++] = arg.getClass();
        try {
            Method m = o.getClass().getMethod(methodName, types);
            m.invoke(o, args);
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException("Error dynamically calling method " + methodName + " on " + o.toString());
     public static void main(String[] args) {
          Callable callee = new Callable();
          callee.callabelMethod(10d);          
          GenericMethodCaller.doCall( callee, "callabelMethod", 10d ); // 10d gets autoboxed to a Double object.
class Callable {
     public void callabelMethod(Double o) {
          System.out.println("callabelMethod(Double o) called");
     public void callabelMethod(double o) {
          System.out.println("callabelMethod(double o) called");
}The output will be:
callabelMethod(double o) called
callabelMethod(Double o) called
- Roy